Add instance of HasVariables for Any f. (#56)

Author: MaximilianAlgehed

quickcheck-dynamic/src/Test/QuickCheck/StateModel/Variables.hs

@@ -1,4 +1,5 @@
 {-# LANGUAGE AllowAmbiguousTypes #-}
+{-# LANGUAGE QuantifiedConstraints #-}
 {-# LANGUAGE UndecidableInstances #-}
 
 module Test.QuickCheck.StateModel.Variables (
@@ -58,6 +59,9 @@ instance (HasVariables k, HasVariables v) => HasVariables (Map k v) where
 instance HasVariables a => HasVariables (Set a) where
   getAllVariables = getAllVariables . Set.toList
 
+instance (forall a. HasVariables (f a)) => HasVariables (Any f) where
+  getAllVariables (Some a) = getAllVariables a
+
 newtype HasNoVariables a = HasNoVariables a
 
 deriving via a instance Show a => Show (HasNoVariables a)